Andrew W.D. Claxson

In vivo absorption, metabolism, and urinary excretion of alpha,beta-unsaturated aldehydes in experimental animals. Relevance to the development of cardiovascular diseases by the dietary ingestion of thermally stressed polyunsaturate-rich culinary oils.

Thermal stressing of polyunsaturated fatty acid (PUFA)- rich culinary oils according to routine frying or cooking practices generates high levels of cytotoxic aldehydic products (predominantly trans-2-alkenals, trans,trans-alka-2,4-dienals, cis,trans-alka-2, 4-dienals, and n-alkanals), species arising from the fragmentation of conjugated hydroperoxydiene precursors. In this investigation we demonstrate that typical trans-2-alkenal compounds known to be produced from the thermally induced autoxidation of PUFAs are readily absorbed from the gut into the systemic circulation in vivo, metabolized (primarily via the addition of glutathione across their electrophilic carbon-carbon double bonds), and excreted in the urine as C-3 mercapturate conjugates in rats. Since such aldehydic products are damaging to human health, the results obtained from our investigations indicate that the dietary ingestion of thermally, autoxidatively stressed PUFA-rich culinary oils promotes the induction, development, and progression of cardiovascular diseases.

Generation of lipid peroxidation products in culinary oils and fats during episodes of thermal stressing: a high field 1H NMR study.

The oxidative deterioration of glycerol‐bound polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (30–90 min at 180°C) has been monitored by high field 1H NMR spectroscopy. Thermal stressing of PUFA‐rich culinary oils generated high levels of n‐alkanals, trans‐2‐alkenals, alka‐2,4‐dienals and 4‐hydroxy‐trans‐2‐alkenals via decomposition of their conjugated hydroperoxydiene precursors, whereas only low concentrations of selected aldehydes were produced in oils with a low PUFA content, lard and dripping when subjected to the above heating episodes. Samples of repeatedly used, PUFA‐rich culinary oils obtained from restaurants also contained high levels of each class of aldehyde. The dietary, physiological and toxicological ramifications of the results obtained are discussed.

Detection of aldehydes and their conjugated hydroperoxydiene precursors in thermally-stressed culinary oils and fats: investigations using high resolution proton NMR spectroscopy.

High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180 degrees C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2,4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.

Multicomponent Spectroscopic Investigations of Salivary Antioxidant Consumption by an Oral Rinse Preparation Containing the Stable Free Radical Species Chlorine Dioxide (CIO2)

A multicomponent evaluation of the oxidative consumption of salivary biomolecules by a commercially-available oral rinse preparation containing an admixture of the stable free radical species chlorine dioxide (ClO2.) with chlorite anion (ClO2-) has been investigated using high resolution 1H NMR spectroscopy. The results obtained demonstrated that ClO2. and/or ClO2- present in this preparation effected the oxidative decarboxylation of salivary pyruvate (to acetate and CO2). Experiments conducted on chemical model systems confirmed the oxidative decarboxylation of pyruvate by this oral rinse, and also demonstrated that urate, thiocyanate anion, and the amino acids cysteine and methionine (precursors to volatile sulphur compounds responsible for oral malodour), were oxidatively consumed. The biochemical, periodontal and therapeutic significance of the results are discussed.

1H-NMR analysis of microbial-derived organic acids in primary root carious lesions and saliva

In addition to lowered pH values, the molecular profile and concentrations of microbial‐derived organic acids in carious dentin are important demineralization parameters involved in the induction, development and progression of dental caries. High‐resolution proton (1H) NMR spectroscopy was employed to examine the organic acid status of primary root carious lesions. 1H‐NMR analysis of post‐neutralized perchloric acid extracts of active carious lesions revealed that at an operating frequency of 600 MHz, the 1H‐NMR‐detectable organic acid composition of carious dentin samples (mean molecular percentage content ± standard error; the mean molecular percentage content is defined here as the mean of the concentration of each 1H‐NMR‐visible organic acid/anion expressed as a percentage of total 1H‐NMR‐detectable organic acid/anion level in each sample) was acetate 51 ± 2%, formate 37 ± 2%, lactate 5 ± 1%, propionate 3 ± 0.8%, pyruvate 2.4 ± 0.3%, n‐butyrate 1.2 ± 0.2%; succinate 0.1 ± 0.1%; iso‐butyrate, n‐ and iso‐valerate, and n‐ and iso‐caproate (total) <0.2%. Further components detectable included alanine, glycine, choline, phosphorylcholine, trimethylamine oxide, methanol, glycolate and assorted saccharides. In view of their high dissociation constants (Ka), our results demonstrate that formic and pyruvic acids (Ka = 1.77 × 10−4 and 3.20 × 10−3 mol/dm3, respectively) contribute substantially to the decreased pH values associated with active caries lesions (cf. lactate Ka = 1.40 × 10−4 mol/dm3), and hence the pathogenesis of primary root caries. Copyright

High resolution proton NMR investigations of rat blood plasma Assignment of resonances for the molecularly mobile carbohydrate side-chains of ‘acute-phase’ glycoproteins

An intense broad resonance at 2.14 ppm present in high field (400, 500 and 600 MHz) Hahn spin‐echo 1H‐NMR spectra of rat blood plasma, but absent from those of human blood plasma is attributable to the presence of terminal O‐acetylsialate sugars in the molecularly mobile carbohydrate side‐chains of ‘acute‐phase’ glycoproteins (predominantly α1‐acid glycoprotein). The presence of such alternative acetylsugars in the carbohydrate side‐chains of rat plasma glycoproteins are of much physiological and experimental significance in view of the regular use of these animals in model systems of human inflammatory conditions.

Assessment of a Human Recombinant Manganese Superoxide Dismutase in Models of Inflammation

We evaluated a novel human recombinant preparation of manganese superoxide dismutase (MnSOD) for anti-inflammatory and anti-oxidant activity compared with a copper zinc (CuZn) SOD preparation. The results showed that administration of MnSOD (50, 100 and 200 micrograms kg-1) in the Freunds Complete Adjuvant (FCA) mediated paw oedema model suppressed the inflammation at 4 hours by 43, 25 and 43% (P < 0.001, P < 0.01 and P < 0.001 at respective doses). However, 24 hours post-challenge, MnSOD (50 and 100 micrograms kg-1), suppressed the inflammation by 19% (P < 0.001). In contrast, Mn SOD at higher doses (400-800 micrograms kg-1; 2 mgkg-1) exacerbated the inflammatory response at 4 hours. This pro-inflammatory response declined progressively by 24 hours. Furthermore, CuZn SOD produced no significant effects on the inflammatory response. In the carrageenan-induced synovitis model, Mn SOD (25 and 50 micrograms; intra-articular administration) exacerbated the inflammation at 48 hours. In contrast, Mn SOD at 5 micrograms produced a significant suppression (44%, P < 0.05) in knee joint swelling at 24 hours. The CuZn SOD preparation produced marked pro-inflammatory effects in the joints whilst it lacked activity in the FCA-mediated paw oedema model. These findings support a therapeutic potential of MnSOD in inflammatory disorders, however the compound has a complex pharmaco-dynamic profile.

The detection of irradiated foodstuffs

Abstract The development of effective test systems for detecting the irradiation of foodstuffs is an essential requirement for the establishment of legislative control and consumer choice. Treatment of foodstuffs with ionizing radiation initially generates extremely reactive free radical species (hydroxyl radicals, hydrated electrons or hydrogen atoms for foodstuffs consisting mainly of water) which cause small, but detectable, chemical changes. This review describes recent advances in the assessment of the irradiation status of foods by methods involving the identification of unique radiolytic products derived from aromatic compounds, DNA and fatty acids. We also review the applications of spectroscopic methods such as thermoluminescence and electron spin resonance spectroscopy in this area. In particular, attention is focused on the recent application of high-field, high-resolution nuclear magnetic resonance (NMR) spectroscopy as a method for distinguishing between irradiated and non-irradiated foodstuffs. Where appropriate, attention is drawn to limitations or potential sources of error in the analytical methods employed.

Multicomponent analysis of radiolytic products in human body fluids using high field proton nuclear magnetic resonance (NMR) spectroscopy

Abstract High field proton Hahn spin-echo nuclear magnetic resonance (NMR) spectroscopy has been employed to investigate radiolytic damage to biomolecules present in intact human body fluids. γ-Radiolysis of healthy or rheumatoid human serum (5.00 kGy) in the presence of atmospheric O 2 gave rise to reproducible elevations in the concentration of NMR-detectable acetate which are predominantly ascribable to the prior oxidation of lactate to pyruvate by hydroxyl radical (·OH) followed by oxidative decarboxylation of pyruvate by radiolytically-generated hydrogen peroxide (H 2 O 2 ) and/or further ·OH radical. Increases in the serum levels of non-protein-bound, low-molecular-mass components such as citrate and glutamine were also observed subsequent to γ-radiolysis, an observation which may reflect their mobilisation from protein binding-sites by ·OH radical, superoxide anion and/or H 2 O 2 . Moreover, substantial radiolytically-mediated elevations in the concentration of serum formate were also detectable. In addition to the above modifications, γ-radiolysis of inflammatory knee-joint synovial fluid (SF) generated a low-molecular-mass oligosaccharide species derived from the radiolytic fragmentation of hyaluronate. The radiolytically-mediated production of acetate in SF samples was markedly greater than that observed in serum samples, a consequence of the much higher levels of ·OH radical-scavenging lactate present. Indeed, increases in SF acetate concentration were detectable at doses as low as 48 Gy. We conclude that high field proton NMR analysis provides much useful information regarding the relative radioprotectant abilities of endogenous components and the nature, status and levels of radiolytic products generated in intact biofluids. We also suggest that NMR-detectable radiolytic products with associated toxicological properties (e.g. formate) may play a role in contributing to the deleterious effects observed following exposure of living organisms to sources of ionising radiation.